Re: Elvis upstreaming plan

[Gleb Natapov <gleb@redhat.com>]

On Wed, Nov 27, 2013 at 11:18:26AM +0200, Abel Gordon wrote:
> 
> 
> Gleb Natapov <gleb@redhat.com> wrote on 27/11/2013 09:35:01 AM:
> 
> > On Wed, Nov 27, 2013 at 10:49:20AM +0800, Jason Wang wrote:
> > > > 4. vhost statistics
> > > > This patch introduces a set of statistics to monitor different
> > performance
> > > > metrics of vhost and our polling and I/O scheduling mechanisms. The
> > > > statistics are exposed using debugfs and can be easily displayed with
> a
> > > > Python script (vhost_stat, based on the old kvm_stats)
> > > > https://github.com/abelg/virtual_io_acceleration/commit/
> > ac14206ea56939ecc3608dc5f978b86fa322e7b0
> > >
> > > How about using trace points instead? Besides statistics, it can also
> > > help more in debugging.
> > Definitely. kvm_stats has moved to ftrace long time ago.
> >
> 
> We should use trace points for debugging information  but IMHO we should
> have a dedicated (and different) mechanism to expose data that can be
> easily consumed by a user-space (policy) application to control how many
> vhost threads we need or any other vhost feature we may introduce
> (e.g. polling). That's why we proposed something like vhost_stat
> based on sysfs.
> 
> This is not like kvm_stat that can be replaced with tracepoints. Here
> we will like to expose data to "control" the system. So I would
> say what we are trying to do something that resembles the ksm interface
> implemented under /sys/kernel/mm/ksm/
There are control operation and there are performance/statistic
gathering operations use /sys for former and ftrace for later. The fact
that you need /sys interface for other things does not mean you can
abuse it for statistics too.

--
			Gleb.